Setup getter and setter elements.

dart/frog/leg/elements/elements.dart

Index: dart/frog/leg/elements/elements.dart
diff --git a/dart/frog/leg/elements/elements.dart b/dart/frog/leg/elements/elements.dart
index add1f013f00ad55dbbf4091f9b326a1619a641d3..d7ad2ef7ef0ddb63d26c55904c916cfa6f10554a 100644
--- a/dart/frog/leg/elements/elements.dart
+++ b/dart/frog/leg/elements/elements.dart
@@ -38,6 +38,8 @@ class ElementKind {
       const ElementKind('generative_constructor_body');
   static final ElementKind COMPILATION_UNIT =
       const ElementKind('compilation_unit');
+  static final ElementKind GETTER = const ElementKind('getter');
+  static final ElementKind SETTER = const ElementKind('setter');
 
   toString() => id;
 }
@@ -73,6 +75,8 @@ class Element implements Hashable {
     return true;
   }
 
+  Token position() => null;
+
   const Element(this.name, this.kind, this.enclosingElement);
 
   // TODO(kasperl): This is a very bad hash code for the element and
@@ -132,6 +136,13 @@ class VariableElement extends Element {
   bool isInstanceMember() {
     return isMember() && !modifiers.isStatic();
   }
+
+  Token position() {
+    // TODO(ahe): Record the token corresponding to name instead of
+    // returning different values at different points in time.
+    return (cachedNode !== null)
+        ? cachedNode.getBeginToken() : variables.position();
+  }
 }
 
 // This element represents a list of variable or field declaration.
@@ -165,6 +176,8 @@ class VariableListElement extends Element {
                    compiler.types);
     return type;
   }
+
+  Token position() => cachedNode.getBeginToken();
 }
 
 class ForeignElement extends Element {
@@ -261,6 +274,8 @@ class FunctionElement extends Element {
   }
 
   Node parseNode(Canceler canceler, Logger logger) => cachedNode;
+
+  Token position() => cachedNode.getBeginToken();
 }
 
 class ConstructorBodyElement extends FunctionElement {
@@ -285,6 +300,8 @@ class ConstructorBodyElement extends FunctionElement {
     assert(cachedNode !== null);
     return cachedNode;
   }
+
+  Token position() => constructor.position();
 }
 
 class SynthesizedConstructorElement extends FunctionElement {
@@ -310,6 +327,8 @@ class SynthesizedConstructorElement extends FunctionElement {
         null, null, null);
     return cachedNode;
   }
+
+  Token position() => null;
 }
 
 class ClassElement extends Element {